Why should the warped stepson inherit wealth over biological kin? I would hope that granddad had a will leaving his estate to his biological children and not his second wife and her gender-confused son.
Most people I know leave a hefty chunk of their estate to the wife so that she can continue living at her previous quality of life
When she dies, what is left over likely will go to her son.
I believe that is the share he is referring to since the grandfather would have no say in what she does with her split. A split likely bigger than the children's